The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:                3GPP third generation partnership project        ABS almost blank subframe        CA carrier aggregation        CE control element        CQI channel quality indicator        CRS common reference signal        DRX discontinuous reception period        DL downlink        E-UTRA evolved universal terrestrial radio access        eICIC enhanced inter-cell interference coordination        eNB evolved NodeB (base transceiver station in LTE/LTE-A)        HARQ hybrid automatic repeat request        LTE long term evolution (evolved UTRAN)        LTE-A LTE-advanced        MAC medium access control        PDCCH physical downlink control channel        PDSCH physical downlink shared channel        PHY physical (logical layer)        PUSCH physical uplink shared channel        RLM radio link measurements        RRC radio resource control        RRM radio resource measurements        RSRP reference signal received power        RTT round trip time        UE user equipment        UL uplink        
Various different wireless radio access technologies specify procedures which are primarily directed toward managing power consumption in user devices which have a limited power supply (for example, galvanic/battery or fuel cell). LTE Release 8 includes the concept of DRX, a per-UE schedule known to both the network and the UE by which the network schedules it DL signaling of radio resource allocations which are relevant to a specific UE only within a certain active window of that UE's DRX cycle. This enables the UE to periodically go to sleep instead of listening continuously for scheduling commands. The purpose of the DRX concept is to improve the UE's energy efficiency; since any given UE typically is not scheduled continuously there would be some natural periods of inactivity. By scheduling periodic inactivity periods the eNB allows the UE to de-power some of its hardware and ongoing processing and thereby extend the time over which the UE's limited power source is sufficient.
In general the DRX mechanism uses a periodic DRX cycle that is composed of two fixed parts: an active part and a sleep part. The active part, which LTE terms Active time, is when the UE is to be ‘awake’ and actively listening to see if the network is sending a PDCCH which schedules the UE for DL and/or UL radio resources. The sleep part, which TE terms the DRX opportunity, is the time the UE might be able to operate in a reduced-power/sleep mode (but there may at times be some scheduled radio resources or ongoing HARQ processes that extends into the DRX opportunity). The convention in LTE at least is that the DRX cycle always begins with an active part, followed by the sleep part after which the cycle begins anew. For the cases noted above in which a scheduled resource or some HARQ process keeps the UE from entering its sleep mode at the usual time given by the DRX cycle, the UE simply extends the active part and correspondingly reduces its sleep part so the next DRX cycle begins on time.
The UE and the network have timers to track the DRX. In LTE the network configures the specific DRX cycle (length, start times) for the UEs. For example, a long DRX might be DRX cycle=640 ms; on duration=10 ms; inactivity timer=5 ms. This DRX configuration would reduce the nominal activity time for the UE to 1/64, (1.56%) as compared to continuous active DL reception or listening. Other radio access technologies use a similar concept which allows the UE to functionally ‘sleep’ for purposes of extending the time over which the radio can operate from its limited power supply. In theory and practice the DRX enables the UE to remain in a power saving mode for most of the time outside heavy activity periods where UE is scheduled continuously.
LTE Release 10 (LTE-A) uses carrier aggregation, in which the whole system bandwidth is divided into multiple component carriers. Since LTE-A contemplates many more network access nodes of various varieties (for example, conventional cells termed macro cells, pico/femto cells/home eNBs, remote radioheads and repeaters) it has also introduced a mechanism to mitigate interference among them, termed enhanced inter-cell interference coordination eICIC. In this technique one cell coordinates with its neighbor cells to avoid interfering transmissions. One aspect of eICIC in LTE Release 10 is almost-blank subframes (ABS), in which a network node transmits nothing except the common reference signals used for measurements (and in some cases also essential control information like synchronization, paging, or system information) but never any unicast DL user data.
In general an eNB transmits its ABSs according to a known pattern and the transmission of the eNB during the ABSs should cause little if any interference to transmissions of neighboring eNBs. The eICIC concept is used for both macro and pico/femto eNBs. A femto eNB may coordinate its transmissions with the overlay macro eNB in order to allow macro user devices close to the femto eNB to experience less interference during the femto eNB's ABS transmissions. Or a macro eNB coordinates its own ABS transmissions with a nearby pico eNB so that the smaller interference from the macro eNB's ABSs allows user devices within a larger area to find and connect to the pico eNB. The ABSs in these coordinated patterns are sent with CRSs, which the user devices use for channel measurement purposes. When eICIC is in use the user device may be instructed to restrict its measurements of the serving cell or of neighbor cells to the configured ABSs. It is also possible to limit the serving cell and neighbor cell measurements according to different patterns.
So the DRX and the eICIC serve widely different purposes: DRX is needed for conserving UE power and is coordinated between the UE and its serving network node; eICIC is needed for making RLM measurements of serving cell and RRM measurements of serving and neighbor cells for handover purposes (for example, RLM measurement restrictions may be used when a small cell and the macro cell interfere with each other and macro cell user is close to the small cell but not able to access the small cell) and is coordinated between adjacent network nodes. It follows that these two procedures are not linked in any way and the inventors see no such linking in the relevant specifications for LTE and LTE-A. The inventors have identified that the eICIC may operate to drastically limit the power savings that the DRX concept enables for a UE. The below teachings restore at least some of the potential power savings at the UE when the DRX is imposed in the presence of measurement restriction patterns due to ABS.